Field
One or more embodiments of the present disclosure relate to a binder composition for a secondary battery, and a cathode and a lithium battery each including the binder composition.
Description of the Related Technology
Lithium batteries are used in various applications due to their high voltage and high energy density. For example, electric vehicles (for example, HEV or PHEV) require lithium batteries with high energy density and excellent lifespan characteristics because batteries for such vehicles are used at high temperature, are charged and discharged of a great amount of electricity, and are used for a long period of time.
To provide lithium batteries with high energy density and excellent lifespan characteristics, an increase in amounts of an electrode active material and a conductive agent and a decrease in an amount of a binder, in an electrode, are required. However, when the amount of the binder decreases, dispersibility and binding force of the electrode active material and/or the conductive agent and flexibility of the electrode active material layer deteriorate. Accordingly, during charging and discharging, an electrode active material may be separated from a current collector, leading to a decrease in cyclic characteristics. Thus, a binder is required that, even in a small amount, provides dispersibility of electrode active material and/or conductive agent, binding force of an electrode plate, and flexibility of an electrode plate, to an electrode.
For example, a fluoropolymer binder, such as a polar functional group-free polyvinylidene fluoride, swells less with respect to an organic electrolytic solution, and thus, when a battery operates, the binder may contribute to maintaining the structure of an electrode and an active material may have improved dispersibility. However, such a fluoropolymer binder shows poor properties in terms of dispersibility of a conductive agent, binding force of an electrode plate, and flexibility of an electrode plate.
Meanwhile, a non fluoropolymer binder, such as an acrylonitrile-acrylic acid-alkylacrylate binder, has higher dispersibility of a conductive agent and flexibility of an electrode plate than the fluoropolymer binder, but its binding force is still low.
Accordingly, a binder is required that has improved binding force and flexibility at the same time to improve energy density and lifespan characteristics of a lithium battery.